I. Field of the Invention
The present invention relates to a method and apparatus for cleaning a printing cylinder, and particularly to a method and apparatus for dry-cleaning the surface of a printing cylinder such as a blanket cylinder or the like.
The surfaces of printing cylinders, particularly blanket cylinders, are generally periodically cleaned because ink sediment and paper powder adhere to the surfaces.
II. Description of The Prior Art
In conventional cleaning methods, the surface of a blanket cylinder is wet-cleaned by using a brush roll impregnated with a cleaning fluid (Japanese Patent Publication No. 44-2166), or a cleaning fluid is sprayed on a contact portion of the surface of a blanket cylinder on which a cleaning sheet is pressed so that the surface is cleaned by relative rotation between the sheet and the blanket cylinder. These are all wet cleaning methods using as a cleaning fluid, a solvent which has affinity for ink and which is impregnated in a brush or sheet for cleaning the surface of a blanket cylinder.
In the conventional cleaning methods, organic solvents must frequently be used for obtaining higher detergency, dangerous substances the use of which is limited by legislation. In addition, since the use of these dangerous substances is restricted from the viewpoint of equipment, the substance is sometimes mixed with flon or the like to lower the flash point and make it less dangerous to handle. However, because of its environmental impact, it is more difficult and may be become impossible to use flon. The disposal of the cleaning fluid, the waste solutions and cleaning sheets impregnated with solvent or the like is therefore a critical problem.
However, methods for cleaning printing cylinders without a solvent for dissolving ink and then wiping off the ink have not been achieved because of the fixed idea that an organic solvent having affinity for the ink must be used for removing ink setoff ad paper powder in tee printing field.
In addition, since the cylinder must be dried after cleaning because the cleaning fluid adheres to the surface of the blanket cylinder, wiping means accompanying the cleaning means must also be provided. Further, an apparatus and equipment must be provided for supplying the cleaning fluid to a brush, a belt and so on. Thus a problem arises with respect to the large space required for the cleaning equipment.
In the case of continuous printing, since printing is not done while supplying paper during a cleaning time, the printing paper passed through the printing cylinder during this time must be discarded as broke. A conventional cleaning method requires at least several minutes or more resulting in discard of may sheets of printing paper as broke. With recent high-speed printing systems the number of broke sheets to be discarded during cleaning is increased.
In addition, the use of a cleaning fluid sometimes causes the cleaning fluid to flow into the inside (rear side serving as a non-printing side) of the blanket through the side or end of the blanket cylinder regardless of whether manual or mechanical cleaning is used. The inside of the blanket is swollen with the cleaning fluid flowing in the inside because the bonded internal surface of the blanket cylinder is generally easily affected by an organic solvent. This frequently results in an increase in the thickness of the blanket and thus abrasion of the print surface, thereby producing a stain on a print. The swelling of the inside of the blanket with a cleaning fluid also causes the problem that the life of the blanket is decreased due to the occurrence of high contact pressure between the blanket and an impression cylinder.